Parkinsonism is a common neurological disorder, particularly in the elderly population. Attempts to use brain transplants as a therapy for Parkinson's disease have been both promising and disappointing. There is relatively small improvement and a gradual deterioration of the beneficial effects after surgery, believed to be due to poor survival of the grafted dopaminergic neurons. My laboratory (Mytilineou et al., 1992) and others (Reynolds and Weiss, 1992) have demonstrated that CNS precursor cells can survive in an arrested phase both in vitro and in vivo and can be stimulated to re-enter the mitotic cycle when treated with epidermal growth factor (EGF). Our recent preliminary studies have indicated that neuronal precursors, already determined to become dopaminergic neurons, can be stimulated by growth factors to continue proliferating in vitro. We propose to study this process of neuronal precursor proliferation as an alternative way to prepare DA neurons for transplantation. Specifically, we have shown that basic fibroblast growth factor (bFGF) stimulates the proliferation of stem cells from the ventral mesencephalon of embryonic day 12 rat brain which differentiate into dopaminergic neurons. Highly homogeneous dopaminergic colonies, consisting of a large number of DA neurons, can be formed by this treatment. When the cell culture conditions do not promote adhesion and differentiation of neuronal precursors, bFGF treatment causes continuous proliferation of the precursor cells, which form cellular spheres in suspension. In our studies, colonies of dividing precursors will be generated in suspension and their differentiation will be studied in vitro and in vivo. The in vivo studies will determine the survival and differentiation of these precursors, when transplanted into the DA-depleted striatum of adult rats, by immunocytochemical analysis with antibodies to tyrosine hydroxylase. The biochemical and functional recovery that may result from these transplants will be examined by HPLC analysis of catecholamine levels in the graftcontaining striata and by comparing the rotational behavior in response to apomorphine or amphetamine before and after transplantation. The ability to maintain, in storage, cells appropriate for brain cell replacement therapy will be a significant advance for brain transplantation in parkinsonian patients and a host of other neurological impairments, where such a therapy is presently either attempted or contemplated.